Acoustic resonator and method of manufacturing the same

ABSTRACT

An acoustic resonator and a method of manufacturing the same are provided. The acoustic resonator includes a resonating part including a first electrode, a second electrode, and a piezoelectric layer; and a plurality of seed layers disposed on one side of the resonating part.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.15/085,072 filed on Mar. 30, 2016, which claims the benefit under 35 USC119(a) of Korean Patent Application No. 10-2015-0181490, filed on Dec.18, 2015 in the Korean Intellectual Property Office, the entiredisclosures of which are incorporated herein by reference for allpurposes.

BACKGROUND 1. Field

The following description relates to an acoustic resonator and a methodof manufacturing the same.

2. Description of Related Art

With the recent trend to miniaturize wireless communications devices,efforts have been made to also reduce radio frequency components thatare used in the wireless communications devices. Film bulk acousticresonators (FBAR) manufactured using semiconductor thin film wafertechnology are an example thereof.

A film bulk acoustic resonator refers to a resonator implemented with athin film element that resonates. The thin film element is generallyobtained by depositing a piezoelectric dielectric material on asemiconductor substrate, such as a silicon wafer, in order to utilizethe piezoelectric characteristics of a piezoelectric dielectricmaterial.

Film bulk acoustic resonators have a wide range of application. Forexample, film bulk acoustic resonators are used as small and lightweight filters for devices such as mobile communications devices,chemical and biological devices, and the like, and as an oscillator, aresonance element, an acoustic resonance mass sensor, and the like.

SUMMARY

This Summary is provided to introduce a selection of concepts in asimplified form that are further described below in the DetailedDescription. This Summary is not intended to identify key features oressential features of the claimed subject matter, nor is it intended tobe used as an aid in determining the scope of the claimed subjectmatter.

In one general aspect, an acoustic resonator includes a resonating partincluding a first electrode, a second electrode, and a piezoelectriclayer disposed between the first electrode and the second electrode, anda plurality of seed layers disposed on one side of the resonating part.

The general aspect of the acoustic resonator may further include asubstrate disposed on the opposite side of the resonating part from theplurality of seed layers.

An air gap may be disposed between the substrate and the plurality ofseed layers.

The resonating part may further include a protection layer.

A membrane may be interposed between the substrate and the plurality ofseed layers, and an air gap may be disposed between the substrate andthe membrane.

The membrane may include a plurality of membrane layers, and at leastone membrane layer of the plurality of membrane layers may be an etchingstopper.

The plurality of seed layers may include a first seed layer and a secondseed layer. The first seed layer may include a material having the samecrystalline system as a material of the piezoelectric layer. The secondseed layer may include a material having the same unit cell geometry asa material of the first seed layer.

A thickness of the first seed layer or the second seed layer may bewithin a range of 10 Å to 1,000 Å.

The piezoelectric layer, the first seed layer, and the second seed layermay each include a material having a hexagonal crystal system.

The piezoelectric layer may include aluminum nitride or doped aluminumnitride. The first electrode may include molybdenum. The first seedlayer may include aluminum nitride. The second seed layer may includetitanium.

An upper surface of the first seed layer may correspond to a (002) planeof hexagonal crystal lattice.

In another general aspect, a method of manufacturing an acousticresonator includes forming a sacrificial layer on a substrate, forming aplurality of seed layers on the substrate or the sacrificial layer,forming a first electrode on the plurality of seed layers, forming apiezoelectric layer on the first electrode, and forming a secondelectrode on the piezoelectric layer.

The general aspect of the method may further include, before the formingof the plurality of seed layers, forming a membrane on the substrate orthe sacrificial layer.

In the forming of the plurality of seed layers, at least one seed layerof the plurality of seed layers may be grown in only a stackingdirection.

The general aspect of the method may further include forming aprotection layer on the second electrode and the piezoelectric layer.

The general aspect of the method may further include forming an air gapby removing the sacrificial layer.

In another general aspect, a method of manufacturing an acousticresonator involves depositing a first electrode on a plurality of seedlayers, and depositing a piezoelectric layer on the first electrode, inwhich the plurality of seed layers includes a first seed layer and asecond seed layer, and the first seed layer and the second seed layerinclude materials having a same unit cell geometry.

The plurality of seed layers may be obtained by depositing the firstseed layer on the second seed layer.

The first seed layer may be deposited on a hexagonal (002) plane of amaterial forming the second seed layer.

The first seed layer or the second seed layer may include a materialthat belongs to the same crystalline system as a material forming thepiezoelectric layer.

The first seed layer may be grown without a polycrystalline growthregion on the first seed layer.

An upper surface of the second seed layer may correspond to a (002)plane of titanium or a (002) plane of aluminum nitride.

Other features and aspects will be apparent from the following detaileddescription, the drawings, and the claims.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a cross-sectional view of an example of an acoustic resonator.

FIG. 2 is an enlarged cross-sectional view illustrating an example of aresonating portion of an acoustic resonator illustrated in FIG. 1.

FIG. 3 is a cross-sectional view of another example of an acousticresonator.

FIG. 4 is an enlarged cross-sectional view illustrating an example of aresonating portion of an acoustic resonator illustrated in FIG. 3.

FIG. 5 is an enlarged cross-sectional view illustrating another exampleof an acoustic resonator.

FIG. 6 is a flowchart illustrating an example of a method ofmanufacturing an acoustic resonator.

Throughout the drawings and the detailed description, the same referencenumerals refer to the same elements. The drawings may not be to scale,and the relative size, proportions, and depiction of elements in thedrawings may be exaggerated for clarity, illustration, and convenience.

DETAlLED DESCRIPTION

The following detailed description is provided to assist the reader ingaining a comprehensive understanding of the methods, apparatuses,and/or systems described herein. However, various changes,modifications, and equivalents of the methods, apparatuses, and/orsystems described herein will be apparent to one of ordinary skill inthe art. The sequences of operations described herein are merelyexamples, and are not limited to those set forth herein, but may bechanged as will be apparent to one of ordinary skill in the art, withthe exception of operations necessarily occurring in a certain order.Also, descriptions of functions and constructions that are well known toone of ordinary skill in the art may be omitted for increased clarityand conciseness.

The features described herein may be embodied in different forms, andare not to be construed as being limited to the examples describedherein. Rather, the examples described herein have been provided so thatthis disclosure will be thorough and complete, and will convey the fullscope of the disclosure to one of ordinary skill in the art.

As noted above, acoustic resonators have a wide range of application.However, various structural shapes and functions for increasingcharacteristics and performances of acoustic resonators, such as a filmbulk acoustic resonators (FBAR), are being researched. For example, ademand exists for modifications to the structure, the material or themanufacturing method of producing film bulk acoustic resonators that maysecure various frequencies and bands.

In order to increase a data transfer amount and a data transfer rate, anacoustic resonator such as a film bulk acoustic resonator (FBAR), forexample, may need to have a wide bandwidth.

In order to secure the wide bandwidth as described above, anelectro-mechanical coupling coefficient (kt2) value of the acousticresonator may need to be increased.

However, because the kt2 value of the acoustic resonator typicallyexists in a trade-off relationship with a quality factor (QF), atechnology that can increase the kt2 value without sacrificing thequality factor is demanded.

As a method of improving the kt2 value, a method of increasingcrystallinity of a piezoelectric layer itself has been researched.

According to an aspect of the present description, an acoustic resonatorcapable of increasing the overall performance by increasingcrystallinity of a piezoelectric material is suggested. According toanother aspect, in order to improve the kt2 value by securingcrystallinity of the piezoelectric layer, a method in which a pluralityof seed layers are added to bottoms of electrodes is suggested.

According to an aspect, an acoustic resonator may include: a resonatingpart including a first electrode, a second electrode, and apiezoelectric layer disposed between the first electrode and the secondelectrode; and a plurality of seed layers disposed on one side of theresonating part, whereby crystallinity of the piezoelectric layer may besecured and an electro-mechanical coupling coefficient (kt2) value ofthe acoustic resonator may be improved.

According to another aspect, a method of manufacturing an acousticresonator may include: forming a sacrificial layer on a substrate;forming a plurality of seed layers on the substrate or the sacrificiallayer; forming a first electrode on the plurality of seed layers;forming a piezoelectric layer on the first electrode; and forming asecond electrode on the piezoelectric layer, whereby an acousticresonator having a high kt2 value may be provided by a simple process

FIG. 1 illustrates a cross-sectional view of an example of an acousticresonator, and FIG. 2 illustrates an enlarged cross-sectional viewillustrating an example of a resonating portion of the acousticresonator illustrated in FIG. 1.

Referring to FIGS. 1 and 2, an acoustic resonator 100 includes aresonating part 120 including a first electrode 121, a second electrode122, and a piezoelectric layer 123 disposed between the first electrodeand the second electrode; and a plurality of seed layers 140 disposed onone side of the resonating part 120.

Further, the acoustic resonator 100 includes a substrate 110 disposed onan opposite side of the plurality of seed layers 140 from the resonatingpart 120.

The substrate 110 may be formed in a silicon substrate or a silicon oninsulator (SOI) type substrate.

In this example, an air gap 130 is formed between the substrate 110 andthe plurality of seed layers 140, and at least a portion of theplurality of seed layers is disposed to be spaced apart from thesubstrate 110 by the air gap 130.

By forming the air gap 130 between the plurality of seed layers 140 andthe substrate 110, an acoustic wave generated from the piezoelectriclayer 123 may not be affected by the substrate.

Further, the reflective characteristics of the acoustic wave generatedfrom the resonating part 120 may be improved by the air gap 130.

Because the air gap 130, which is an empty space, has an impedance thatis close to infinity, the acoustic wave may remain in the resonatingpart 120 while not being lost by the air gap.

Therefore, the loss of the acoustic wave in a longitudinal direction maybe significantly reduced by the air gap 130. As a result, a qualityfactor (QF) of the resonating part 120 may be improved.

The resonating part 120 includes the first electrode 121, the secondelectrode 122, and the piezoelectric layer 123 as described above. Theresonating part 120 may be formed by sequentially laminating the firstelectrode 121, the piezoelectric layer 123, the second electrode 122from below.

When the layers are formed in this order, the piezoelectric layer 123 isdisposed between the first electrode 121 and the second electrode 122.

The resonating part 120 may make the piezoelectric layer 123 resonate inresponse to electrical signals applied to the first electrode 121 andthe second electrode 122 to generate a resonance frequency and ananti-resonance frequency.

The first electrode 121 and the second electrode 122 may be formed of ametal such as gold, molybdenum, ruthenium, aluminum, platinum, titanium,tungsten, palladium, chrome, nickel, iridium, or the like.

The resonating part 120 may use the acoustic wave of the piezoelectriclayer 123. For example, in response to signals being applied to thefirst electrode 121 and the second electrode 122, mechanical vibrationmay occur in a thickness direction of the piezoelectric layer 123 togenerate the acoustic wave.

The piezoelectric layer 123 may be formed of a piezoelectric materialsuch as zinc oxide (ZnO), aluminum nitride (AlN), silicon dioxide(SiO₂), doped zinc oxide (e.g., W—ZnO), doped aluminum nitride (e.g.,Sc—AlN, MgZr—AlN, Cr—AlN, Er—AlN, Y—AlN), or the like.

A resonance phenomenon of the piezoelectric layer 123 may occur inresponse to a half of a wavelength of the applied signal matching athickness of the piezoelectric layer.

Because the electrical impedance sharply changes in response to theoccurrence of resonance phenomenon, the acoustic resonator according tothis embodiment may be used as a filter capable of selecting afrequency.

The resonance frequency may be determined by the thickness of thepiezoelectric layer 123, the inherent acoustic wave velocity of thepiezoelectric layer 123, the first electrode 121 and the secondelectrode 122 that surround the piezoelectric layer 123, and the like.

In general, in response to the thickness of the piezoelectric layer 123being reduced, the resonance frequency is increased.

Further, because the piezoelectric layer 123 is disposed only in theresonating part 120, a phenomenon in which the acoustic wave generatedby the piezoelectric layer is leaked externally from the resonating partmay be significantly reduced.

In this example, the resonating part 120 further includes a protectionlayer 124.

The protection layer 124 covers the second electrode 122 to prevent thesecond electrode 122 from being exposed to an external environment.However, the present description is not limited thereto.

In this example, the first electrode 121 and the second electrode 122extend to an outer side of the piezoelectric layer 123, and a firstconnection part 180 and a second connection part 190 are each connectedto the extended portion.

The first connection part 180 and the second connection part 190 may beprovided to confirm characteristics of the resonator and the filter andperform a required frequency trimming, but are not limited thereto.

The plurality of seed layers 140 are disposed on one side of theresonating part 120, that is, below the first electrode 121.

The plurality of seed layers 140 includes a first seed layer 141 and asecond seed layer 142, and the first seed layer and the second seedlayer may be obtained by being sputtered on a planarized substrate 110or a sacrificial layer (not illustrated).

The first seed layer 141 may be manufactured using aluminum nitride(AlN), doped aluminum nitride (e.g., Sc—AlN, MgZr—AlN, Cr—AlN, Er—AlN,Y—AlN), or other similar crystalline materials, such as aluminumoxynitride (AlON), silicon dioxide (SiO₂), silicon nitride (Si₃N₄),silicon carbide (SiC), and the like.

In an example, the first seed layer 141 is formed of aluminum nitride(AlN). The second seed layer 142 is formed of a material having the samecrystalline system or Bravais lattice system as the material forming thefirst seed layer 141. For example, aluminum nitride (AlN) has ahexagonal crystal system. Thus, in the event that the first seed layer141 is formed of aluminum nitride (AlN), the second seed layer 142 maybe formed of a metal of a hexagonal system having unit cells of the samegeometry, such as magnesium (Mg), titanium (Ti), zinc (Zn), and thelike.

FIGS. 1 and 2 illustrate an example in which the first seed layer 141 isstacked on the second seed layer 142, but the order of stacking thefirst and second seed layers is not limited thereto. On the contrary,the second seed layer may be stacked on the first seed layer.

In this example, at least one of the seed layers is formed of apiezoelectric material so as not to serve as an electrode and rather toserve as a piezoelectric layer, thereby affecting the piezoelectriccharacteristics of the piezoelectric layer 123.

As a result, in the event that a film thickness of the seed layersbecomes too thick, an influence on piezoelectric characteristics of thepiezoelectric layer may be increased. Thus, according to one example, athickness of the first seed layer 141 may be set within a range of about10 Å to 1,000 Å so that the influence on piezoelectric characteristicsis not increased more than necessary.

Further, the second seed layer 142 formed of a metal that belongs to thehexagonal crystal system or having the same crystal lattice structuresuch as titanium, or the like, may need to be grown in only a (001)direction, that is, a stacking direction. However, if a thickness of thesecond seed layer 142 is grown to be 1,000 Å or more, the second seedlayer 142 may also be grown in a (010) direction in addition to a (001)direction, thereby increasing a lattice mismatch with the first seedlayer 141.

Eventually, because a growth in a (010) direction causes deteriorationin crystallinity of the first electrode 121 and the piezoelectric layer123 grown on the second seed layer 142, according to one example, thethickness of the second seed layer 142 is also set to 1,000 Å or less inwhich the second seed layer 142 is grown in only a (001) direction, thatis, the stacking direction.

In order to increase the crystallinity of the piezoelectric layer 123,the crystallinity of the first electrode 121 disposed below thepiezoelectric layer 123 may need to be secured. To this end, accordingto one example, a plurality of seed layers 140 is used below the firstelectrode.

For example, in the event that a piezoelectric layer 123 is formed ofaluminum nitride (AlN) and the first electrode 121 is formed ofmolybdenum, a thin film of the piezoelectric layer formed of aluminumnitride may initially show polycrystalline growth characteristics, andmay then be aligned in a (001) direction in which the growth speed isthe fastest.

In the event that the first electrode 121 formed of molybdenum is grownwithout using any seed layers, the crystallinity of the piezoelectriclayer 123 formed of aluminum nitride that is deposited on the firstelectrode 121 may also deteriorate due to the defects in the crystallinestructure of the molybdenum first electrode 121.

However, in an example, by utilizing a first seed layer 141 formed ofaluminum nitride, an aluminum nitride seed starts to grow in a (001)direction, that is, the stacking direction, there by securing a highercrystallinity of the first electrode 121 formed of molybdenum, and ahigher crystallinity of the piezoelectric layer 123 formed of aluminumnitride disposed on the first electrode 121.

As such, in this example, the piezoelectric layer 123 exhibits excellentcrystallinity, and the kt2 value of the acoustic resonator 100 isincreased.

Meanwhile, because aluminum nitride (002) and molybdenum (110) have avery large lattice mismatch of 12.45%, a method of increasingpiezoelectric characteristics by increasing the thickness of thepiezoelectric layer formed of aluminum nitride may be applied; however,due to a size limit imposed on the acoustic resonators, there exists alimit in increasing the piezoelectric characteristics by using themethod of increasing the thickness of the piezoelectric layer until thepolycrystalline growth gradually shifts to a single-crystal growth.

However, because a lattice mismatch between molybdenum (110) andtitanium (002) is only 7.64%, an excellent crystallinity may be securedfor a molybdenum layer by juxtaposing a titanium seed layer.

In an example, a molybdenum layer may be aligned in a (110) crystallineplane direction. An excellent crystallinity for an aluminum nitridelayer may be obtained by forming the aluminum nitride layer on amolybdenum layer exposing the (110) plane.

According to an X-ray diffraction test, it may be seen that whentitanium is grown in only a (001) direction, that is, the stackingdirection, and molybdenum and aluminum nitride are deposited ontitanium, aluminum nitride is grown in only a (001) direction andmolybdenum is grown in only a (110) direction, similar to whenmolybdenum and aluminum nitride are deposited on the aluminum nitrideseed, thereby securing improved crystallinity of the piezoelectric layeras compared to the case in which only the aluminum nitride seed is used.

Further, it may be seen that the lattice mismatch between aluminumnitride (002) and titanium (002), which is 5.49%, is lower than thelattice mismatch between molybdenum (110) and titanium (002), which is7.64%.

Further, it may be seen that because aluminum nitride and titanium havethe same hexagonal system, excellent crystallinity may be secured whentwo materials are stacked on each other.

Therefore, according to an example, in order to improve the kt2 value bysecuring crystallinity of the piezoelectric layer 123, the second seedlayer 142 formed of, for example, titanium, or the like, having a lowlattice mismatch, that is, the plurality of seed layers, may be disposedbelow the first seed layer 141 formed of, for example, aluminum nitride,or the like.

According to one example, a second seed layer 142 formed of titaniumhaving the low lattice mismatch is employed below the first seed layer141 formed of aluminum nitride. Because titanium is grown in a (001)direction, that is, the stacking direction, and titanium (002) andaluminum nitride (002) have the low lattice mismatch, the first seedlayer formed of aluminum nitride may be directly grown in a (001)direction, that is, the stacking direction without an initialpolycrystalline growth.

As a result, high crystallinity of the first seed layer 141 formed ofaluminum nitride (002) may be secured, and crystallinity of the firstelectrode 121 formed of molybdenum (110) and the piezoelectric layer 123formed of aluminum nitride (002) grown on the first seed layer 141 maybe improved. As a result, a high kt2 value may be obtained withoutincreasing loss in the acoustic wave.

FIG. 6 illustrates an example of a method of manufacturing an acousticresonator.

First, a sacrificial layer is formed on a substrate 110 in 610. As amaterial for the sacrificial layer, silicon dioxide, polysilicon,polymer, or the like may be used.

The sacrificial layer may be removed later by an etching process to forman air gap 130. The shape of the sacrificial layer may conform to theshape of the air gap 130 to be formed later.

Next, a plurality of seed layers 140 may be sequentially formed on thesubstrate 110 and the sacrificial layer in 620. A technology and aprocess of manufacturing the seed layers widely known in the art, suchas a sputtering technology, may be used to manufacture the seed layers.

By properly controlling process conditions of the sputtering that isperformed such as, for example, a temperature, the degree of a vacuum,strength of power, an amount of injected gas, and the like, theplurality of seed layers 140 may be grown in only a (001) direction,that is, the stacking direction.

As such, in an example in which most of the plurality of seed layers areoriented in a desired direction, that is, a (001) direction, when thepiezoelectric layer 123 is formed on the plurality of seed layers 140 asdescribed below, the piezoelectric layer may succeed a crystal structureof the seed layers 140 to be oriented in the same crystal structure asthe seed layers 140.

According to one example, the first seed layer 141 may be formed ofaluminum nitride (AlN), but is not limited thereto. For example, variousmaterials such as silicon dioxide (SiO₂), silicon nitride (Si₃N₄),silicon carbide (SiC), aluminum oxynitride (AlON), and the like may beused.

Further, the second seed layer 142 may be formed of titanium (Ti), butis not limited thereto. For example, a metal such as magnesium, zinc, orthe like may be used.

In an example of a filter that includes a plurality of resonators, asecond seed layer 142 may need to be selectively formed in only thepredetermined resonator that requires a high kt2 value. Thus, the secondseed layer 142 may be left on only a predetermined portion of the filterby performing a patterning after forming the second seed layer usingtitanium by the sputtering, and the following processes may beperformed.

According to an example, the second seed layer 142 may be formed of amaterial having a hexagonal close packed structure such as titanium(Ti), magnesium (Mg), zinc (Zn), or the like, before the first seedlayer 141. For example, a titanium seed layer having a thickness of 10to 1000 Å may be formed directly on a Si substrate. The crystalorientation of the second seed layer comprised of titanium deposited bya sputtering method may be controlled in order to expose substantially a(002) plane of its hexagonal lattice. When the thickness of the titaniumseed layer exceeds 1000 Å, the growth along a (010) plane of the latticeincreases, thereby increasing dislocation.

On an upper surface corresponding to a (002) plane of titanium layer,the first seed layer 141 may be grown. The first seed layer 141 may bean aluminum nitride (AlN) layer, but the present description is notlimited thereto. For example, various materials such as silicon dioxide(SiO₂), silicon nitride (Si₃N₄), silicon carbide (SiC), aluminumoxynitride (AlON), and the like may be used.

A first seed layer 141 comprised of aluminum nitride (AlN) may be grownwith high crystallinity on a (002) plane of a titanium layer because thelattice mismatch is low. The aluminum nitride (AlN) seed layer may bedeposited by a sputtering method to expose a (002) plane of itshexagonal lattice. By forming the second seed layer 141 of titanium(002) prior to forming the first seed layer 141 of aluminum nitride(002), it is possible to prevent an initial polycrystalline growth ofaluminum nitride on a silicon substrate. Accordingly, the plurality ofseed layers 140 makes it possible to secure high crystallinity forsubsequent layers deposited thereon.

Thereafter, the first electrode 121 and the piezoelectric layer 123 aresequentially formed on the plurality of seed layers 140.

In 630, the first electrode 121 is formed. The first electrode 121 maybe formed by depositing a conductive layer on the seed layers 140.Similarly, in 640, the piezoelectric layer 123 may be formed bydepositing a piezoelectric material on the first electrode 121.

In the illustrated embodiment, the first electrode 121 may be formed ofa molybdenum (Mo) material, but is not limited thereto. For example,various metals such as gold, ruthenium, aluminum, platinum, titanium,tungsten, palladium, chrome, nickel, iridium, and the like may be used.

According to one example, a first electrode 121 composed of molybdenum(Mo) is deposited on a (002) plane of a first seed layer 141 formed ofaluminum nitride (AlN), the first seed layer 141 deposited on a (002)plane of a second seed layer 142 formed of titanium (Ti), For instance,the first electrode 121 of molybdenum (110) may be grown on a first seedlayer 142 formed of a (002) oriented aluminum nitride layer.

Further, the piezoelectric layer 123 may be formed of aluminum nitride(AlN), but is not limited thereto. For example, various piezoelectricmaterials such as zinc oxide (ZnO), silicon dioxide (SiO₂), doped zincoxide (e.g., W—ZnO), doped aluminum nitride (e.g., Sc—AlN, MgZr—AlN,Cr—AlN, Er—AlN, Y—AlN), and the like may be used.

According to one example, a piezoelectric layer 123 formed of aluminumnitride (AlN) may be formed on a first electrode 121 of Mo (110) formedon a first seed layer 141 of AlN (002) and a second seed layer 142 of Ti(002). A high crystallinity piezoelectric layer 123 may be obtained bycontrolling the crystalline orientation at the interface between thefirst seed layer 141 and the second seed layer 142, the first seed layer141 and the first electrode 121, and the first electrode 121 and thepiezoelectric layer 123.

The first electrode 121 and the piezoelectric layer 123 may be formed ina predetermined pattern by depositing a photoresist on the conductivelayer or the piezoelectric layer, performing the patterning using aphotolithography process, and then removing unnecessary portions usingthe patterned photoresist as a mask.

Thereby, the piezoelectric layer 123 may be left on only the firstelectrode 121. As a result, the first electrode may be left to furtherprotrude around the piezoelectric layer.

Next, the second electrode 122 is formed in 650.

The second electrode 122 may be formed in a predetermined pattern byforming the conductive layer on the piezoelectric layer 123 and thefirst electrode 121, depositing the photoresist on the conductive layer,performing the patterning using the photolithography process, and thenremoving unnecessary portions using the patterned photoresist as themask.

According to one example, the second electrode 122 may be formed ofruthenium (Ru), but is not limited thereto. For example, various metalssuch as gold, molybdenum, aluminum, platinum, titanium, tungsten,palladium, chrome, nickel, iridium, and the like may be used.

Next, the protection layer 124 is formed on the second electrode 122 andthe piezoelectric layer 123 in 660.

The protection layer 124 may be formed of an insulating material.Examples of the insulating material include silicon oxide basedmaterials, silicon nitride based materials, and aluminum nitride basedmaterials.

Thereafter, the connection parts 180 and 190 are formed in 670. Theconnection parts 180 and 190 may be used for a frequency trimming.

The first connection part 180 and the second connection part 190 maypenetrate through the protection layer 124 to be bonded to the firstelectrode 121 and the second electrode 122, respectively.

The first connection part 180 may be formed by partially removing theprotection layer 124 by the etching to form a hole, externally exposingthe first electrode 121, and then depositing gold (Au), copper (Cu), orthe like on the first electrode.

Similarly, the second connection part 190 may also be formed bypartially removing the protection layer 124 by the etching to form thehole, externally exposing the second electrode 122, and then depositinggold (Au), copper (Cu), or the like on the second electrode.

After confirming characteristics of the resonating part 120 or thefilter and performing a frequency trimming as desirable using theconnection parts 180 and 190, the air gap 130 may be formed.

The air gap 130 may be formed by removing the sacrificial layer asdescribed above. As a result, the resonating part 120 may be completed.

Here, the sacrificial layer may be removed by a dry etching, but is notlimited thereto.

For example, the sacrificial layer may be formed of polysilicon. Such asacrificial layer may be removed by dry etching gas such as xenondifluoride (XeF₂).

Meanwhile, the acoustic resonator and the method of manufacturing thesame according to the present disclosure are not limited to theabove-mentioned embodiments, and may be variously modified.

FIG. 3 illustrates a cross-sectional view of another example of anacoustic resonator, and FIG. 4 illustrates an enlarged cross-sectionalview of a main part of the acoustic resonator illustrated in FIG. 3.

Referring to FIGS. 3 and 4, an acoustic resonator 200 includes aresonating part 120 including a first electrode 121, a second electrode122, and a piezoelectric layer 123 disposed between the first electrodeand the second electrode; a plurality of seed layers 140 disposed on oneside of the resonating part; and a membrane 150 disposed on the oppositeside of the resonating part from the seed layers.

The remaining components of the acoustic resonator illustrated in FIG. 3are the same as those described above with reference to FIGS. 1 and 2,except that the membrane 150 is disposed below the plurality of seedlayers 140.

Thus, in describing the acoustic resonator 200 according to anotherexample, the same components as those of the acoustic resonator 100 aredenoted by like reference numerals.

Referring to FIGS. 3 and 4, the acoustic resonator 200 further includesthe substrate 110 disposed on an opposite side of the plurality of seedlayers 140 from the resonating part 120. In addition, the membrane 150is interposed between the plurality of seed layers 140 and the substrate110.

The substrate 110 may be formed in a silicon substrate or a silicon oninsulator (SOI) type substrate.

The air gap 130 is formed between the substrate 110 and the membrane150, and at least a portion of the membrane may be disposed to be spacedapart from the substrate by the air gap.

Further, because the resonating part 120 is formed on the membrane 150,the resonating part may also be spaced apart from the substrate 110 bythe air gap 130.

By forming the air gap 130 between the substrate 110 and the membrane150, an acoustic wave generated from the piezoelectric layer 123 may notbe affected by the substrate.

Further, reflective characteristics of the acoustic wave generated fromthe resonating part 120 may be improved by the air gap 130.

Because the air gap 130, which is an empty space, has impedance that isclose to infinity, the acoustic wave may remain in the resonating part120 while not being lost by the air gap 130.

Therefore, loss of the acoustic wave in a longitudinal direction may besignificantly reduced by the air gap 130. As a result, a quality factor(QF) of the resonating part 120 may be improved.

In this example, the membrane 150 is positioned on the air gap 130 tomaintain a shape of the air gap 130 and to provide structural support tothe resonating part 120.

The membrane 150 may be formed of silicon dioxide (SiO₂), or the like.

As described below, in an example in which the air gap 130 is formed byetching the sacrificial layer, the membrane may be formed of a pluralityof membrane layers so that the membrane 150 may serve as an etchingstopper.

For example, referring to FIG. 5, the membrane 150 includes a firstmembrane layer 151 formed of, for example, silicon dioxide (SiO₂), and asecond membrane layer 152 formed of, for example, silicon nitride(SiN_(x)) and formed on the first membrane layer.

Of course, a stop layer 160 serving as the etching stopper may also beformed on the substrate to protect the substrate 110, and the stop layermay include silicon oxide (SiO_(x)), silicon nitride (SiN_(x)), or thelike.

The resonating part 120 includes the first electrode 121, thepiezoelectric layer 123, and the second electrode 122, as describedabove, and the resonating part 120 may be obtained by sequentiallylaminating the first electrode, the piezoelectric layer, and the secondelectrode from below.

The resonating part 120 may make the piezoelectric layer 123 resonate inresponse to electrical signals applied to the first electrode 121 andthe second electrode 122 to generate a resonance frequency and ananti-resonance frequency.

The first electrode 121 and the second electrode 122 may be formed of ametal such as gold, molybdenum, ruthenium, aluminum, platinum, titanium,tungsten, palladium, chrome, nickel, iridium, or the like.

The resonating part 120 may use the acoustic wave of the piezoelectriclayer 123. For example, in response to signals being applied to thefirst electrode 121 and the second electrode 122, mechanical vibrationmay occur in a thickness direction of the piezoelectric layer 123 togenerate the acoustic wave.

The piezoelectric layer 123 may be formed of a piezoelectric materialsuch as zinc oxide (ZnO), aluminum nitride (AlN), silicon dioxide(SiO₂), doped zinc oxide (e.g., W—ZnO), doped aluminum nitride (e.g.,Sc—AlN, MgZr—AlN, Cr—AlN, Er—AlN, Y—AlN), or the like.

In the illustrated example, the resonating part 120 further includes theprotection layer 124.

The protection layer 124 covers the second electrode 122 to prevent thesecond electrode from being exposed to an external environment.

The first electrode 121 and the second electrode 122 extend to an outerside of the piezoelectric layer 123, and the first connection part 180and the second connection part 190 are each connected to the extendedportion.

The first connection part 180 and the second connection part 190 may beprovided to confirm characteristics of the resonator and the filter andto perform a required frequency trimming, but are not limited thereto.

The plurality of seed layers 140 are disposed between the resonatingpart 120 and the membrane 150, that is, below the first electrode 121and on the membrane 150.

The plurality of seed layers 140 includes the first seed layer 141 andthe second seed layer 142, and the first seed layer and the second seedlayer may be deposited by being sputtered on a planarized substrate 110or a sacrificial layer (not illustrated).

The first seed layer 141 may be manufactured using aluminum nitride(AlN), doped aluminum nitride (e.g., Sc—AlN, MgZr—AlN, Cr—AlN, Er—AlN,Y—AlN), or other similar crystalline materials, such as aluminumoxynitride (AlON), silicon dioxide (SiO₂), silicon nitride (Si₃N₄),silicon carbide (SiC), and the like.

In an example, the first seed layer is formed of aluminum nitride (AlN),and the second seed layer 142 is formed of a material having the samecrystalline lattice structure with the first seed layer 141. Forexample, the second seed layer 142 may be formed of a metal of ahexagonal lattice system having the same unit cell geometry, such asmagnesium (Mg), titanium (Ti), zinc (Zn), and the like.

FIGS. 3 through 5 illustrate examples of acoustic resonators in whichthe first seed layer 141 is stacked on the second seed layer 142, butthe order of stacking the first and second seed layers is not limitedthereto. On the contrary, the second seed layer may be stacked on thefirst seed layer.

In these examples, at least one of the seed layers 140 is formed of apiezoelectric material so as not to serve as an electrode and rather toserve as a piezoelectric layer, thereby affecting the piezoelectriccharacteristics of the piezoelectric layer 123.

In the event that a film thickness of the seed layers becomes too thick,an influence on piezoelectric characteristics of the piezoelectric layer123 may be increased. Thus, according to these examples, a thickness ofthe first seed layer 141 is set within the range of about 10 Å to 1,000Å so that the influence on piezoelectric characteristics is notincreased more than desirable.

Further, the second seed layer 142 formed of the metal of the hexagonalsystem such as titanium, or the like, may need to be grown in only a(001) direction, that is, a stacking direction. However, in the eventthat a thickness of the second seed layer 142 is grown to be 1,000 Å ormore, the second seed layer 142 may also be grown in a (010) directionin addition to a (001) direction, thereby increasing a lattice mismatchwith the first seed layer 141.

Because growing a thick layer eventually causes a deterioration in thecrystallinity of the first electrode 121 and the piezoelectric layer 123grown on the second seed layer 142, according to one example, thethickness of the second seed layer 142 is set to be 1,000 Å or less suchthat the second seed layer 142 is grown in only a (001) direction, thatis, the stacking direction.

In order to increase the crystallinity of the piezoelectric layer 123,the crystallinity of the first electrode 121 disposed below thepiezoelectric layer 123 may need to be secured. To this end, accordingto one example, the plurality of seed layers 140 are used below thefirst electrode.

In this example, in order to improve the kt2 value by securing thecrystallinity of the piezoelectric layer 123, the second seed layer 142formed of, for example, titanium, or the like, having a low latticemismatch, that is, the plurality of seed layers, may be disposed belowthe first seed layer formed of, for example, aluminum nitride, or thelike.

According to one example, a second seed layer 142 formed of titanium isemployed below a first seed layer 141 formed of aluminum nitride.Because titanium is grown in a (001) direction, that is, the stackingdirection, and titanium and aluminum nitride have a low latticemismatch, the first seed layer formed of aluminum nitride may bedirectly grown in a (001) direction, that is, the stacking directionwithout an initial polycrystalline growth.

As a result, a high crystallinity is secured for the first seed layer141 formed of aluminum nitride, and the crystallinity of the firstelectrode 121 formed of molybdenum and the piezoelectric layer 123formed of aluminum nitride grown on the first seed layer 141 isimproved. Thus, a high kt2 value may be obtained without increasing lossin the acoustic wave.

Hereinafter, another example of a method of manufacturing an acousticresonator will be described.

First, a sacrificial layer (not illustrated) may be formed on thesubstrate 110, as in 610 of FIG. 6. As a material for the sacrificiallayer, silicon dioxide, polysilicon, polymer, or the like may be used.

The sacrificial layer may be removed later by an etching process to formthe air gap 130.

Next, a membrane 150 may be formed on the substrate 110. The membrane150 may be deposited on the substrate 110 and the sacrificial layer.

As a method of forming the membrane 150, a proper method may be selectedand used among deposition methods such as a chemical vapor deposition(CVD) method, a sputtering method, and the like, depending on a materialthat forms the membrane 150.

Further, according to one example, as the membrane, a first membranelayer 151 formed of, for example, silicon dioxide (SiO₂) may be formed,and a second membrane layer 152 formed of, for example, silicon nitride(SiN_(x)) may be formed on the first membrane layer.

In addition, a plurality of seed layers 140 may be sequentially formedon the membrane 150. A technology or process of manufacturing the seedlayers widely known in the art, such as a sputtering technology, may beused to manufacture the seed layers.

According to one example, by properly controlling the process conditionsof the sputtering, such as a temperature, the degree of a vacuum,strength of power, an amount of injected gas, and the like, theplurality of the seed layers 140 may be grown in only a (001) direction,that is, the stacking direction.

As such, in an example in which most of the plurality of seed layers areoriented in a desired direction, that is, a (001) direction, when thepiezoelectric layer 123 is formed on the plurality of seed layers 140 asdescribed below, the piezoelectric layer may succeed a crystal structureof the seed layers 140 to be oriented in the same crystal structure andorientation as the seed layers 140.

According to one example, the first seed layer 141 may be formed ofaluminum nitride (AlN), but is not limited thereto. For example, variousmaterials such as silicon dioxide (SiO₂), silicon nitride (Si₃N₄),silicon carbide (SiC), aluminum oxynitride (AlON), and the like may beused.

Further, according to another example, the second seed layer 142 may beformed of titanium (Ti), but is not limited thereto. For example, ametal such as magnesium (Mg), zinc (Zn), or the like may be used.

Thereafter, the first electrode 121 and the piezoelectric layer 123 maybe sequentially formed on a plurality of seed layers 140.

The first electrode 121 may be formed by depositing a conductive layeron the seed layers 140. Similarly, the piezoelectric layer 123 may beformed by depositing a piezoelectric material on the first electrode.

According to another example, the first electrode 121 may be formed of amolybdenum (Mo) material, but is not limited thereto. For example,various metals such as gold, ruthenium, aluminum, platinum, titanium,tungsten, palladium, chrome, nickel, iridium, and the like may be used.

Further, according to one example, the piezoelectric layer 123 may beformed of aluminum nitride (AlN), but is not limited thereto. Forexample, various piezoelectric materials such as zinc oxide (ZnO),silicon dioxide (SiO₂), doped zinc oxide (e.g., W—ZnO), doped aluminumnitride (e.g., Sc—AlN, MgZr—AlN, Cr—AlN, Er—AlN, Y—AlN), and the likemay be used.

In this example, the first electrode 121 and the piezoelectric layer 123may be formed in a predetermined pattern by depositing a photoresist onthe conductive layer or the piezoelectric layer, performing thepatterning using a photolithography process, and then removingunnecessary portions using the patterned photoresist as a mask.

Thereby, the piezoelectric layer 123 may be left on only the firstelectrode 121. As a result, the first electrode may be left to furtherprotrude around the piezoelectric layer 123.

Next, the second electrode 122 may be formed.

The second electrode 122 may be formed in a predetermined pattern byforming the conductive layer on the piezoelectric layer 123 and thefirst electrode 121, depositing the photoresist on the conductive layer,performing the patterning using the photolithography process, and thenremoving unnecessary portions using the patterned photoresist as themask.

According to another example, the second electrode 122 may be formed ofruthenium (Ru), but is not limited thereto. For example, various metalssuch as gold, molybdenum, aluminum, platinum, titanium, tungsten,palladium, chrome, nickel, iridium, and the like may be used.

The protection layer 124 may also be formed on the second electrode 122and the piezoelectric layer 123.

Further, the first connection part 180 and the second connection part190 may penetrate through the protection layer 124 to be bonded to thefirst electrode 121 and the second electrode 122, respectively.

After confirming characteristics of the resonating part 120 or thefilter and performing any necessary frequency trimming using theconnection parts 180 and 190, the air gap 130 may be formed.

The air gap 130 may be formed by removing the sacrificial layer asdescribed above. As a result, the resonating part 120 according toanother example may be completed.

In this example, the sacrificial layer may be removed by a dry etching,but the present description is not limited thereto.

According to one example, the sacrificial layer is formed ofpolysilicon. Such a sacrificial layer may be removed by using a dryetching gas such as xenon difluoride (XeF₂).

When the air gap 130 is formed by etching the sacrificial layer, in theevent that the membrane 150 is formed of a plurality of membrane layers,a second membrane layer 152 formed on a first membrane layer 151 mayserve as an etching stopper to protect the plurality of seed layers 140formed on the second membrane layer 152 from being etched.

The first membrane layer 151 may be formed of, for example, silicondioxide (SiO₂), or the like, and the second membrane layer 152 may beformed of, for example, silicon nitride (SiN_(x)), or the like. However,the present description are not limited thereto.

Meanwhile, the acoustic resonator and the method of manufacturing thesame according to the present description are not limited to theabove-mentioned embodiments, and may be variously modified.

As set forth above, according to an example of an acoustic resonator,because high crystallinity of the piezoelectric layer may be secured,the loss in the acoustic wave may be significantly reduced, and the kt2value and performance of the acoustic resonator may be improved.

While this disclosure includes specific examples, it will be apparent toone of ordinary skill in the art that various changes in form anddetails may be made in these examples without departing from the spiritand scope of the claims and their equivalents. The examples describedherein are to be considered in a descriptive sense only, and not forpurposes of limitation. Descriptions of features or aspects in eachexample are to be considered as being applicable to similar features oraspects in other examples. Suitable results may be achieved if thedescribed techniques are performed in a different order, and/or ifcomponents in a described system, architecture, device, or circuit arecombined in a different manner, and/or replaced or supplemented by othercomponents or their equivalents. Therefore, the scope of the disclosureis defined not by the detailed description, but by the claims and theirequivalents, and all variations within the scope of the claims and theirequivalents are to be construed as being included in the disclosure.

What is claimed is:
 1. An acoustic resonator comprising: a resonatingpart comprising a first electrode, a second electrode, and apiezoelectric layer disposed between the first electrode and the secondelectrode; and a plurality of seed layers disposed on one side of theresonating part.
 2. The acoustic resonator of claim 1, furthercomprising a substrate disposed on the opposite side of the resonatingpart from the plurality of seed layers.
 3. The acoustic resonator ofclaim 2, wherein an air gap is disposed between the substrate and theplurality of seed layers.
 4. The acoustic resonator of claim 2, whereinthe resonating part further comprises a protection layer.
 5. Theacoustic resonator of claim 2, wherein a membrane is interposed betweenthe substrate and the plurality of seed layers, and an air gap isdisposed between the substrate and the membrane.
 6. The acousticresonator of claim 5, wherein the membrane comprises a plurality ofmembrane layers, and at least one membrane layer of the plurality ofmembrane layers is an etching stopper.
 7. The acoustic resonator ofclaim 1, wherein the plurality of seed layers comprise a first seedlayer and a second seed layer, the first seed layer comprises a materialhaving the same crystalline system as a material of the piezoelectriclayer, and the second seed layer comprises a material having the sameunit cell geometry as a material of the first seed layer.
 8. Theacoustic resonator of claim 7, wherein a thickness of the first seedlayer or the second seed layer is within a range of 10 Å to 1,000 Å. 9.The acoustic resonator of claim 7, wherein the piezoelectric layer, thefirst seed layer, and the second seed layer each comprise a materialhaving a hexagonal crystal system.
 10. The acoustic resonator of claim9, wherein the second seed layer comprises a material having a hexagonalclose packed structure.
 11. The acoustic resonator of claim 9, whereinthe piezoelectric layer comprises aluminum nitride or doped aluminumnitride, the first electrode comprises molybdenum, the first seed layercomprises aluminum nitride, and the second seed layer comprisestitanium.
 12. The acoustic resonator of claim 7, wherein an uppersurface of the second seed layer corresponds to a (002) plane ofhexagonal lattice.
 13. The acoustic resonator of claim 7, wherein thepiezoelectric layer comprises aluminum nitride or doped aluminumnitride, the first electrode comprises molybdenum, the first seed layercomprises titanium, and the second seed layer comprises aluminumnitride.
 14. The acoustic resonator of claim 1, wherein the plurality ofseed layers comprise a first seed layer and a second seed layer; whereina lattice mismatch between the first seed layer and the second seedlayer is less than or equal to 7.64%.
 15. The acoustic resonator ofclaim 1, wherein the plurality of seed layers comprise a first seedlayer and a second seed layer; wherein a lattice mismatch between thefirst seed layer and the second seed layer is 5.49%.
 16. An acousticresonator comprising: a resonating part comprising a first electrode, asecond electrode, and a piezoelectric layer disposed between the firstelectrode and the second electrode; and a plurality of seed layersdisposed on one side of the resonating part, wherein a first seed layerand a second seed layer of the plurality of seed layers, and thepiezoelectric layer each comprise a material having a hexagonal crystalsystem.
 17. The acoustic resonator of claim 16, wherein the second seedlayer comprises a material having a hexagonal close packed structure.18. The acoustic resonator of claim 16, wherein the piezoelectric layercomprises aluminum nitride or doped aluminum nitride, the firstelectrode comprises molybdenum, the first seed layer comprises aluminumnitride, and the second seed layer comprises titanium.
 19. The acousticresonator of claim 16, wherein the piezoelectric layer comprisesaluminum nitride or doped aluminum nitride, the first electrodecomprises molybdenum, the first seed layer comprises titanium, and thesecond seed layer comprises aluminum nitride.
 20. An acoustic resonatorcomprising: a resonating part comprising a first electrode, a secondelectrode, and a piezoelectric layer disposed between the firstelectrode and the second electrode; a plurality of seed layers disposedon one side of the resonating part; a substrate disposed on the oppositeside of the plurality of seed layers from the resonating part; and aplurality of membrane layers interposed between the substrate and theplurality of seed layers.